The present invention relates to methods and apparatus for joining planar plastic members at corners and, more particularly, to an improved solventless joint for plastic wherein conventional glue and solvent adhesion of the joint is replaced with stapling.
The side members of an air filter housing of conventional construction as manufactured and sold by the assignee of this application is shown in simplified form in FIG. 1 and labelled therein as 10. The housing 10 comprises two L-shaped planar plastic members 12 which, when joined opposite edge to opposite edge, form the ends 14, top 16, and bottom 18 of the housing 10. While not important to the present invention, a pair of rectangular grills (not shown) are fit into grooves (also not shown) provided on the inner surfaces of the L-shaped members 12 adjacent the edges and an air filtering element (not shown) is also assembled into the housing 10 at the time of assembly.
A detailed cutaway side view of a prior art joint 22 as where the top 16 of one L-shaped member 12 is attached to the end 14 of the other L-shaped member 12 is shown in FIGS. 2-4. The top 16 is generally planar and made of a thin, tough sheet 24 of plastic. A planar lip 26 surrounds the sheet 24 at right angles thereto as shown in FIG. 2. The end 14 is of similar construction again being generally planar and made of a thin, tough sheet 28 of plastic. A planar lip 30 again surrounds the sheet 28 at right angles thereto as also shown in FIG. 2. A plurality of cylindrical guide pins 32 extend outward perpendicular to the lip 26 along the length of the joint 22. A plurality of guide pin receiving blocks 34 are molded into the area under lip 30 behind the sheet 28 opposite the guide pins 32. As best seen in the cutaway views of FIG. 3 and 4, the guide pin receiving blocks 34 each have a hole 36 formed therein for receiving the guide pins 32. It should be noted at this point that the construction being described herein (both as to the prior art and the present invention hereinafter) is accomplished by injection molding of the parts. Thus, the two L-shaped members 12 and the two grills 20 are each of unitary construction; that is, there are only four parts in the air filter housing 10 and two9 joints of concern.
Turning now with particularity to FIGS. 3 and 4, at the time of assembly, the face of lip 26 having the guide pins 32 extending outward therefrom may be coated with an adhesive 38 as depicted in FIG. 3. As an alternative, the opposed surfaces to be joined may be coated with a plastic solvent such as that referred to as MEK which causes temporary softening of the surfaces and subsequent bonding thereof. The parts are then pressed together as depicted in FIG. 4. The guide pins 32 are received by the holes 36 to align the top 16 with the end 14 both vertically and laterally. In principle, such prior art joint construction is satisfactory. In commercial application, however, such prior art joint construction has numerous shortcomings. First, it is very labor intensive. The adhesive 38 must be applied and then the components assembled before the adhesive 38 sets up. If one of the components is mis-fit and the adhesive 38 (or solvent) is of a rapid drying variety, the error may not be correctable without destroying the joint 22. If a slower drying adhesive or solvent is employed, the joints 22 must be held together until the adhesive sets up or the solvent softened plastic hardens sufficiently to hold together; if not, the joint 22 may move out of position and set up in a mis-fit state. A low adhesion adhesive or solvent puts much of the physical strength of the joint 22 on the guide pins 32--which were designed for guidance during assembly only, not strength. As a result, if the housing 10 is bumped or dropped, the pins 32 at one or both joints 22 may shear off, thus just as effectively destroying the joint 22.
As an additional consideration, there are certain applications for a plastic articles (such as the air filter housing for which the present invention was developed) where the use of adhesives and solvents is undesirable for various reasons such as sanitation, potential odor, etc.
Wherefore, it is the object of the present invention to provide a solventless joint construction and method of assembly for use in joining planar plastic members at corners such as in the case of hollow plastic housings for air filter housings, and the like, which is strong and of low labor intensity.